WASM tracking

[stoically]

• EventEmitter and CryptoStore: Probably requires an alternative trait without Send + Sync (Do wasm sepcific changes #60)
• Sleeping panics: Possibly wasm-timer could help fix that. Also Instant is using the instant crate but wasm-timer provides an Instant as well, so could get potentially changed
• Switch to crates.io version of futures-locks once a new version gets published (Release 0.5.1 asomers/futures-locks#38) (matrix-sdk-common: Switch futures-locks to crates.io version #94)
• Open PRs to allow olm to compile
  • libolm make target
  • Move rust-crypto to dev-dependencies engineerd/cjson#1
  • BrainBlasted/olm-sys#8
• CryptoStore needs an IndexedDB Implementation to work reliably (prototype: indexeddb-cryptostore) (IndexedDB support for wasm/browser environments #414)

Extracted from: #31 (review)

[stoically]

A possible workaround for the Send+Sync issue could be a macro attribute like

#[cfg_attr(not(target_arch = "wasm32"), send_sync)]

which adds the bound for non-wasm targets.

[MTRNord]

Required proc macro: (Requires syn and quote crates)

use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, parse_quote, ItemTrait};

/// Attribute to use `Send + Sync` for everything but wasm32
#[proc_macro_attribute]
pub fn send_sync(_attr: TokenStream, input: TokenStream) -> TokenStream {
    // Parse the input tokens into a syntax tree
    let mut input = parse_macro_input!(input as ItemTrait);

    let send_trait_bound = parse_quote!(std::marker::Send);
    let sync_trait_bound = parse_quote!(std::marker::Sync);
    input.supertraits.push(send_trait_bound);
    input.supertraits.push(sync_trait_bound);

    TokenStream::from(quote!(#input))
}

[MTRNord]

And a specific macro for async_trait on EventEmitter as the send_sync macro doesn't work:

/// A wasm32 compatible wrapper for the async_trait::async_trait macro
#[proc_macro_attribute]
pub fn async_trait(_attr: TokenStream, item: TokenStream) -> TokenStream {
    let attrs = r#"
        #[cfg_attr(target_arch = "wasm32", async_trait::async_trait(?Send))]
        #[cfg_attr(not(target_arch = "wasm32"), async_trait::async_trait)]
    "#;

    let mut out: TokenStream = attrs.parse().unwrap();
    out.extend(item);
    out
}

it replaces #[async_trait::async_trait] and Send + Sync can get removed

[MTRNord]

Also the async_trait macro needs to be used on all impl. You might use async_trait::async_trait in non wasm targets directly and can also use on things that only compile to wasm32 async_trait::async_trait(?Send). Just the main definition of EventEmitter needs to use this macro (or the attribures)

[poljar]

I forgot to mention this over here, but we have a prototype CryptoStore that uses indexeddb over here.

It uses a fork of indexeddb-rs since the upstream one doesn't compile, fork is over here.

[stoically]

Closing as all boxes are checked. Thanks @gnunicorn for the missing piece.